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Improved N use efficiency (NUE) increases wheat (Triticum aestivum L.) yields and reduces N losses in the environment. We investigated genetic variation and correlations among agronomic and NUE traits in Canada Western Red Spring wheat cultivars to further improve NUE. Trials were conducted for 3 yr at two locations in Alberta, Canada, under two levels of N (200 and ~50 kg ha−1). Genotype × environment interaction was significant for traits associated with vegetative growth, and genotype × N fertilizer treatment interaction was significant for important yield and NUE traits. There were significant positive correlations between total dry matter and N uptake efficiency (NUpE) in the high (r = 0.74, P < 0.05) and low (r = 0.83, P < 0.05) N treatments. The effect of dwarfing Rht‐1b allele was more prominent under high N treatment in increasing NUE. However, cultivars with Rht‐1b allele showed inconsistent results for NUpE, indicating that Rht alleles might have pleiotropic effects on N uptake. Grain yield, NUE, and N utilization efficiency (NUtE) exhibited genetic improvement over time only under high N treatment. Our results indicated that grain yield increased mainly due to improved harvest index (HI), suggesting improvement in C assimilation rather than N partitioning efficiency. Nitrogen use efficiency may further be improved by intercrossing cultivars with high HI, N harvest index, and NUtE and those with good NUpE, while using total dry matter production as a selection criterion.

. 2015. The effect of weeds on soil arbuscular mycorrhizal fungi and agronomic traits in spring wheat (Triticum aestivum L.) under organic management in Canada. Can. J. Plant Sci. 95: 615Á627. Understanding the influence of weeds in agroecosystems may aid in developing efficient and sustainable organic wheat production systems. We examined the effect of weeds on soil microbial communities and the performance of spring wheat (Triticum aestivum L.) under organic management in Edmonton, AB, Canada. We grew 13 Canadian spring wheat cultivars in organically managed hand-weeded less-weedy and weedy treatments in 2010 and 2011. The less-weedy treatment exhibited greater grain yield and tillers per square meter, while kernel weight, test weight, days to maturity, plant height, grain P and protein content were not altered by weed treatment. Canada Western Red Spring (CWRS) wheat cultivars CDC Go and CDC Kernen were the most yield-stable because they minimized fertile tiller reduction in response to weed pressure (10 and 13% reduction, respectively, compared with the average reduction of 20%). Other cultivars exhibited yield stability through increased kernel weight. The contribution of arbuscular mycorrhizal fungi (AMF) to the total phospholipid fatty acid increased in both treatments; however, the rate of this increase was greater in the weedy treatment than the less-weedy treatment (from 2.9 to 3.9%, from 2.8 to 3.1%, respectively). Weed dry biomass was positively correlated with AMF% in the less-weedy treatment only. Organic systems tend to be weedier than conventional systems. We found that weeds are important determinants of AMF proliferation in soil. In addition, choosing wheat cultivars that maintain important yield components under severe weed stress is one strategy to maximize yields in organic systems.Key words: Organic agriculture, wheat (spring), arbuscular mycorrhizal fungi, weed Kubota, H., Quideau, S. A., Hucl, P. J. et Spaner, D. M. 2015. Incidence des mauvaises herbes sur la mycorhizes a`arbuscules dans le sol et sur les parame`tres agronomiques du ble´de printemps (Triticum aestivum L.) cultive´de fac¸on biologique au Canada. Can. J. Plant Sci. 95: 615Á627. Comprendre l'influence des adventices dans les e´cosyste`mes agricoles pourrait faciliter l'e´laboration de syste`mes de production efficaces et durables pour la culture biologique du ble´. Les auteurs ont examine´l'impact des mauvaises herbes sur la microflore du sol et sur le rendement du ble´de printemps (Triticum aestivum L.) cultive´de fac¸on biologique a`Edmonton, en Alberta (Canada). À cette fin, ils ont cultive´biologiquement treize varie´te´s canadiennes de ble´de printemps sur des parcelles de´sherbe´es a`la main ou envahies de mauvaises herbes en 2010 et en 2011. Les parcelles de´sherbe´es ont produit plus de grain et de talles par m 2 , mais les mauvaises herbes ne modifient pas le poids du grain, le poids spe´cifique, le nombre de jours jusqu'a`maturite´, la hauteur du plant, la teneur en P du grain ni la concentration de prote´ines. Les...

Better management of synthetic nitrogen (N) fertilizers in conventional agricultural systems laid the foundation for feeding the increasing world's population since the Green Revolution. However, excessive reliance on inorganic fertilizer has resulted in environmental degradation issues. Difficulties in soil nutrition management in organic cropping systems often results in lower and variable yields, also raising questions of sustainability. Improving nitrogen use efficiency (NUE) is thus of key importance to overcome environmental concerns in conventional systems and production limitations in organic systems. The differences in the two farming systems have impacts on crop traits and N cycles, making it difficult to enhance NUE with a single strategy. Different approaches need to be adopted to improve NUE in each system. Extensive efforts have been made to better understand mechanisms to potentially improve NUE in cereal crops under both systems. This review suggests that NUE may be improved through a combination of management practices and breeding strategies specific to the management system. Diversified crop rotations with legumes are effective practices to optimize the N cycle in both conventional and organic systems. Best Management Practices coupled with nitrification inhibitors, controlled release products and split-application practices can reduce N loss in conventional systems. In organic systems, we need to take advantage of available N sources and adapt practices such as no-tillage, cover crops, and catch crops. Utilization of beneficial soil microorganisms is fundamental to optimizing availability of soil N. Estimation of soil organic matter mineralization using prediction models may be useful to enhance NUE if models are calibrated for target environments. Cereal crops are often bred under optimum N conditions and may not perform well under low N conditions. Thus, breeders can integrate genetic and phenotypic information to develop cultivars adapted to specific environments and cultivation practices. The proper choice and integration of strategies can synchronize N demand and supply within a system, resulting in reduced risk of N loss while improving NUE in both conventional and organic systems.

There is debate regarding direct or indirect selection for organic conditions. Our objective was to evaluate the progress of indirectly selecting organic cultivars in conventional environments. Canadian spring wheat (Triticum aestivum L.) cultivars, developed for conventional environments from 1885 to 1999 and from 1975 to 2009, respectively, were grown in two separate experiments to assess progress of yield and associated agronomic traits due to breeding. The first experiment evaluated 27 cultivars in organic and conventional conditions for 3 yr (2002, 2003, and 2004), on three sites in western Canada. In the second experiment, eight cultivars were evaluated in organic conditions in 2010 and 2011 at the University of Alberta, Canada. The first experiment showed that breeding had improved yield and most associated traits only in conventional systems and a few associated traits in organic conditions. The second experiment showed that breeding had made significant improvements in yield and test weight in organic conditions. This study suggests that with sufficient quality and disease resistance criteria in place for the breeding of wheat in conventional environments, it may be possible to concomitantly improve wheat yield destined for organic growing conditions. However, fewer associated traits showed significant improvement in organic conditions and improvement rates were lower than in conventional conditions. This suggests that optimizing trait performance in organic conditions should include organic conditions during breeding and selection.